Phylogeographic Structure Of The Seaweed Agarophyton Vermiculophyllum(Gigartinales,Rhodophyta)in The Northwest Pacific And Conservation Applications

The northwest Pacific is one of the regions with the richest marine biodiversity in the world,and the repeated transgression and regression of coastlines mediated by the late Quaternary glacial-interglacial cycles make this region a hotspot to study marine speciation and population genetic diversity.With the interference of global climate change and anthropogenic activities,the distribution ranges of species in the northwest Pacific are shrinking and the diversity levels are being destroyed continuously,highlighting the importance and necessity of conserving natural marine resources.The red alga Agarophyton vermiculophyllum(Ohmi)Gurgel,J.N.Norris et Fredericq is a commercially and ecologically important foundation species native to the northwest Pacific,and it taxonomically belongs to Agarophyton,Gracilariaceae,Gracilariales,Florideophyceae,Rhodophyta.In addition,A.vermiculophyllum has caught extensive research interest because of its widespread invasion in Europe and North America.However,the knowledge of phylogeographic structure and genetic diversity across the entire native range are still scarce.In this study,we used mitochondrial cytochrome c oxidase subunit 1(cox1)and microsatellite(SSR)to explore phylogeographic patterns and population genetic differentiation of A.vermiculophyllum in the northwest Pacific.The main results are as follows:(1)We used cox1 sequence(1214bp)to explore the phylogeographic patterns,population diversity and genetic differentiation of 48 A.vermiculophyllum populations(611 individuals)in the northwest Pacific.The results showed high haplotype diversity(H_d=0.6632)and low nucleotide diversity(?=0.2473×10^-2)in A.vermiculophyllum in the northwest Pacific,and the Japanese populations had the highest genetic diversity.The phylogenetic analysis of cox1 haplotypes based on Bayesian Inference(BI)and Maximum Likelihood(ML)consistently revealed five phylogeographically structured genetic lineages that diverged significantly from each other.The divergence time among the five genetic lineages varied from 0.02 to 0.05Ma.Among all pairwise comparisons of 48 populations,most were differentiated significantly(70.8%F_st>0.25,p<0.05).S-DIVA analyses showed that the ancestors of A.vermiculophyllum in the northwest Pacific was widely distributed in three biogeographic areas including the Japan-Pacific coast,the East China Sea(Okinawa trough)and the South China Sea during the ice age.These combined evidence indicate that A.vermiculophyllum might have survived in multiple scattered glacial refugia during the late Quaternary climate oscillations in the northwest Pacific.(2)We additionally used 10 microsatellites(SSR)to explore the genetic structure and diversity of 38 A.vermiculophyllum populations(555 individuals)in the northwest Pacific.Totally,126 alleles were obtained with an average effective allele of 4.290,and small values of other genetic parameters indicate a relatively low genetic diversity in A.vermiculophyllum in the northwest Pacific.F_is(0.3455)and F_it(0.7303)indicated a certain degree of inbreeding and heterozygote loss.Structure analysis detected four genetic groups.In particular,a rare genetic isolationwas found in the southeast of Shandong peninsula,and the sea of Japan and the Japanese population clustered into a genetic group with obvious genetic mixing.F_st(0.5879),Nei's genetic distance and N_m(0.1752)showed significant genetic differentiation and weak gene flow between A.vermiculophyllum populations.In addition to palaeoclimate oscillations and ocean current,reproduction patterns,selection pressure imposed by microgeographical environmental variables and human interference may be related to these genetic characteristics detected in A.vermiculophyllum in the northwest Pacific.This study systematically described population genetic structure,diversity and temporal-spatial lineage distribution of A.vermiculophyllum in the northwest Pacific,including the underlying factors contributing to such a distribution pattern.The results not only lay a foundation for further exploring the invasion route and genetic mechanism of A.vermiculophyllum inhabiting different ecological niches,but also provide scientific basis for conserving and managing natural resources of it.